Inflation is the rate of change in the relative purchase power of money, or equivalently the price of goods and services, over time. Metrics such as the consumer price index and the retail price index have come about to track the cumulative prices of one or more select baskets of goods and/or services over time in order to gain some measure of the amount of inflation in an economy. Inflation may be considered by investors in making various kinds of investments, inasmuch as it may affect the actual value of an investment or amount of returns received. For example, a quantity of money invested in a low-interest bank account may actually be losing value over time if the interest rate on the account is outpaced by the inflation rate. Some financial instruments, such as Treasury Inflation-Protected Securities (TIPS) have come about to provide investment opportunities that neutralize any adverse inflationary effects.